Data is stored on magnetic media by writing on the magnetic media using a write head. Magnetic media may be formed in any number of ways, such as tape, floppy diskette, hard disk, or the like. Writing involves storing a data bit by utilizing magnetic flux to set the magnetic moment of a particular area on the magnetic media. The state of the magnetic moment is later read, using a read head, to retrieve the stored information.
Conventional thin film read heads employ magnetoresistive material, generally formed in a layered structure of magnetoresistive and non-magnetoresistive materials, to detect the magnetic moment of the bit on the media. A sensing current is passed through the magnetoresistive material to detect changes in the resistance of the material induced by the bits as the media is moved with respect to the read head.
Magnetoresistive read heads use permanent magnet layers for stabilizing the response of the device as well as setting the quiescent state of the device. In current-in-the plane or CIP devices, such as anisotropic magnetoresistive and spin valve devices, the permanent magnet is formed contiguous with a magnetoresistive element and is used to set the magnetization of the magnetoresistive element in a longitudinal direction by pinning the magnetization at each end of the magnetoresistive element stripe. This prevents formation of closure domains at the ends of the element. Without pinning, movement of the end domains can cause hysteresis in the magnetoresistive response of the device.
A conventional method for making the permanent magnet layer in an anisotropic magnetoresistive and spin valve read sensors involves the formation of a contiguous junction as the result of a lift-off process, for example, as disclosed in U.S. Pat. No. 5,079,035, by Krounbi et al., issued Jan. 7, 1992, entitled METHOD OF MAKING A MAGNETORESISTIVE READ TRANSDUCER HAVING HARD MAGNETIC BIAS, and in U.S. Pat. No. 5,664,316, by Chen et al., issued Sept. 9, 1997, entitled METHOD OF MANUFACTURING MAGNETIRESISTIVE READ TRANSDUCER HAVING A CONTIGUOUS LONGITUDINAL BIAS LAYER, both herein incorporated by reference in their entireties.
In such a process, layers of the magnetoresistive material are deposited on a substrate. A reentrant bi-layer resist, consisting of a thin underlayer and a thick imaging layer, is formed on the magnetoresistive material. An exposure and a develop step define the edge of the resist and unmasks regions of the magnetoresistive layers. Use of an appropriate developer dissolves the underlayer forming an undercut. The size of the undercut is determined by the develop time.
The magnetoresistive material is ion beam etched, to form the magnetoresistive element. Layers are deposited adjacent the magnetoresistive element to form the contiguous junction. Typically, these adjacent layers can consist of an underlayer, such as Cr, a permanent magnet material, such as CoCrPt, and a lead layer, such as Au. The permanent magnet and leads taper as they approach the contiguous junction and may overhang the top of the magnetoresistive device as illustrated in the patents referenced above.
The present inventors have noted several problems with such a configuration. The extremely thin lead material on top of the magnetoresistive element does not provide a low resistance current path. The actual current density profile could be quite complex, leading to ambiguity in the actual effective track width of the magnetoresistive element.
In addition, the combined effects of the taper and the overhang can cause a decrease, of the permanent magnet induced longitudinal field, from the center to the edge of the magnetoresistive device. This will cause the formation of domain walls which affect the stability of the device. Even where the magnet does not overlay the magnetoresistive material, the tapered end of the permanent magnet decreases the thickness of the remnant magnetization Mr of the magnet near the edge of the magnetoresistive device, thus reducing the stabilizing effect of the magnet.
In a current perpendicular-to-the plane or CPP device such as a multilayer giant magnetoresistive device, the quiescent state of the device has antiparallel magnetic alignment of the magnetoresistive element layers for maximum resistance. A bias permanent magnet is used to shift the relative magnetization angle between layers 45 degrees so that the device operates in the middle of the linear region. The magnet is placed on the side of the stack, away from the air bearing surface at a separation which achieves the proper biasing, as disclosed in U.S. Pat. No. 5,784,224, by Rottmayer and Zhu, issued Jul. 21, 1998, herein incorporated by reference in its entirety.
In the current perpendicular-to-the plane multilayer device, a tapered magnet overlaying the magnetoresistive material is unacceptable. The magnet and the magnetoresistive material must be insulated from each other. Also, the magnetoresistive material and the magnet must be separated so that the biasing field is relatively uniform along the height of the magnetoresistive material and so that the side of the magnetoresistive element nearest the permanent magnet is not pinned. The field must be uniform since the field from the permanent magnet is the only means to properly bias the device. These requirements place even more stringent limits on the configuration of the permanent magnet than with contiguous junction CIP devices. As such, preventing permanent magnet taper and overhang in CPP devices is even more critical to optimizing performance of the device.
The preferred method and structure of the present invention allows for an improved bias magnet-to-magnetoresistive element interface to improve the longitudinal bias of a magnetoresistive element.
In a contiguous junction embodiment of the present invention, the magnetoresistive element has vertical side walls formed by over etching to remove side wall taper. When forming the side walls, a portion of the underlying layer is etched forming a cavity in the underlying layer. A magnetic bias material layer may be deposited so that it abuts the side wall to form a contiguous junction with the magnetoresistive element. It is preferred to form the magnetic bias layer so that its top and bottom surfaces are generally aligned, or spaced further apart so that the magnetoresistive element is aligned within the bias layer. Such a junction improves the domain structure within the magnetoresistive element, particularly near the edge of the magnetoresistive element.
In a typical embodiment, a reentrant resist structure, such as a bilayer resist structure is used to pattern deposition of the magnetic bias material. In such a case, portions of the bias material may form under the overhang of the resist structure to form tapered portions overhanging the magnetoresistive element. In such embodiments, the overhanging taper portion/portions may be removed using directional etching.
Also with this embodiment, a protective element is formed on, or over, the magnetoresistive element prior to bias material deposition to protect the element during etch processes. In the preferred embodiments, the protective element is formed from a layer of protective material, such as inorganic insulation material, along with formation of the magnetoresistive element.
It is possible with such embodiments, to deposit a filler layer in the cavity prior to bias layer formation. In such a case, any portion forming on the side walls of the magnetoresistive element may be etched using directional etching techniques known in the art to allow contiguous joining of the magnetoresistive element and the bias layer. Also with this embodiment, the protective element is employed to protect the magnetoresistive element during etching of the side wall filler layer material.
In CPP embodiments of the present invention, the magnetoresistive element is formed with a vertical back wall displaced from an air bearing surface. The back wall is formed by over etching to remove back wall taper as in the contiguous junction embodiments.
In CPP embodiments, however, the filler layer is deposited on the back wall prior to bias layer formation to insulate the magnetoresistive element from the bias layer. As with the contiguous junction embodiments, a taper portion of the bias layer may form under the overhang of the resist structure and overhang the magnetoresistive element. The overhanging taper portion may be removed using a directional etching.
As with contiguous junction embodiments, it is preferred to form the magnetic bias layer so that its top and bottom surfaces are at least generally aligned, or spaced further apart so that the magnetoresistive element is aligned within the bias layer. Also, as with the contiguous junction embodiments, it is preferred that bias layer have a generally parallel wall opposing the back wall of the magnetoresistive element, albeit insulated from the back wall.
Also with this embodiment, a protective element is formed, as in the contiguous junction embodiments, on, or over, the magnetoresistive element to protect the element during etching of the overhanging taper portion.
Removing side or back wall taper and the overhanging taper portions/portion improves the direction and stability of the induced longitudinal field within the magnetoresistive element.
In addition, in some contiguous junction embodiments, tapered overhang removal allows for the formation of improved lead structures. As the bias layer does not overhang the magnetoresistive element, lead material may be deposited on the top surface of the magnetoresistive element closer to side walls. In addition, the leads are not pinched off by the overhanging taper portion of the underlying bias layer. As such, the magnetoresistive element-to-lead interface of these embodiments improves current density profile and improves definition of the actual effective track width of the device.